a) Field of the Invention
The present invention is directed to a special illumination unit for generating a variable slit image such as is used in ophthalmological examination instruments, including slit lamps. A light section is generated by slit image projection in the more or less transparent object under examination, e.g., in the interior of the eye. The parameters of the section bundle are variable, particularly the angle of incidence, the dimensions of the slit image, its intensity and the spectral composition. Information about the object under examination can be acquired from the shape, position and intensity of the scattered light of the sectional image generated in this way.
b) Description of the Related Art
In slit lamps such as those described in Rassow, B. et al., “Ophthalmologic-optical instruments”, 1987, Ferdinand Enke Verlag Stuttgart, pages 99ff and 137ff, mechanical/optical elements such as slit diaphragms have been used up until now to generate slit imaging. The variable, smallest possible slit widths which are required for high optical detail resolution within the optical section are very difficult to achieve. Further, the mechanical component groups are very cumbersome to adjust, and this is made even more difficult by the thermal expansion of the component groups, among other things. Reproducibility of adjustments for measurement purposes is possible only to a limited extent. The multiplicity of possible illuminated field geometries is extremely limited by the fixed slit diaphragms and pinhole diaphragms and the space required by the latter.
Since slit image projection involves optical imaging with a physically defined depth of focus, the imaging must always be focused strictly on the point of examination. A section bundle which is focused over the entire extension of the human eye can not be achieved with the solutions mentioned above. While conditions can be improved with an arrangement based on the Scheimpflug principle, the technical expenditure is correspondingly greater.
DE 198 12 050 A1 describes a method and an arrangement for illumination in an ocular microscope. A wide variety of illuminating mark geometries is generated by means of opto-electronic components. The illuminated field geometries are projected on the anterior portion and fundus of the eye and are used for general examination of the eye.
Methods and arrangements for illuminating the anterior segments of the eye in which a planar configured laser is used as light source are described in U.S. Pat. Nos. 5,404,884, 5,139,022 and 6,275,718. However, in these solutions the limited variability of the slit dimensions, the utilized wavelength of the laser sources, and the lack of a possibility for generating multiple-slit projections are disadvantageous under certain circumstances. The described arrangements are not slit lamp devices used in normal diagnostic operation. Further, the system for receiving the scattered light from the eye has a physically limited depth of focus which can not completely acquire the expansion area of the sharp sectional laser image.